The present invention relates generally to passively alignable opto-electronic coupling assemblies and more particularly to an opto-electronic coupling assembly in which an active device is passively aligned with an end face of an elongated light guide. An associated method is also disclosed.
Optical communication systems utilizing light conductive members such as, for example, fiber optic cables are increasingly popular for reasons including, but not limited to very high bandwidth capabilities. Light transmitted by fiber optic cables is, in most instances, produced by a light emitting semiconductor device which is optically coupled to an end face of the fiber optic cable.
In the prior art, significant attention has been devoted to opto-electronic assemblies which optically couple a semiconductor device with a fiber optic cable. Of course, such opto-electronic assemblies must provide proper support for the semiconductor device. Other provisions must be made for electrical interfacing and heat dissipation. One paramount requirement resides in achieving proper optical alignment (i.e., efficient light coupling) between the output of the semiconductor device and the input face of the fiber optic cable. In this regard, many prior art assemblies employ an "active" alignment approach in which a trained technician or automated assembly equipment actually performs one or more alignment adjustments on each assembly. It should be appreciated that the active alignment approach adds considerable cost to the manufacturing process. Therefore, a "passive" alignment approach is generally preferred in which no alignment adjustments are required. However, for reasons to be discussed immediately hereinafter, it is submitted that few if any practical and inexpensive passive alignment approaches have been provided in the prior art.
Alignment difficulties are introduced both by characteristics of fiber optic cables and by characteristics of various types of light producing semiconductor devices used in the assembly. With regard to fiber optic cables, it should be appreciated that the "target" (i.e., input face) of a typical cable is quite small. For example, the input face of a multi-mode fiber is typically 50 microns in diameter, however, diameters up to 125 microns are available for glass fibers. As another example, the input face of a single mode fiber is a mere 5 microns in diameter. Thus, the difficulties of passive alignment begin to become evident in view of fiber input face diameters alone.
Semiconductor devices which are useful in opto-electronic assemblies include light emitting diodes (LED's), edge emitting lasers (one group being referred to as CD lasers) and Vertical Cavity Surface Emitting Lasers (hereinafter VCSEL's). Relevant characteristics of these light producing devices will be discussed at appropriate points hereinafter. For the moment, it is sufficient to say that light emission characteristics and certain other characteristics such as, for example, moisture resistance vary significantly between these various device types. The relevant characteristics of these devices must be considered in coupling any of them with a fiber optic cable in any sort of alignment scheme, including that of passive alignment.
The present invention provides a light coupling arrangement and associated method which incorporate a highly advantageous passive optical alignment feature and which is particularly well suited for use with individual or arrayed light emitting devices amenable to plastic encapsulation.